Vehicle interior panels sometimes include a layer of foam material sandwiched between a thin decorative layer and an underlying structural layer to provide a composite structure with a cushion-like feel when a vehicle occupant touches and presses on the visible surface of the assembled and installed interior panel. One technique for forming such a foam layer is via introduction of a liquid foam precursor between the desired layers. The foam precursor includes a mixture of liquids formulated to chemically react once distributed between the desired layers. The reaction results in volumetric expansion of the mixture and, finally, in a solid polymeric material with tiny gas voids distributed throughout the material—i.e., a foam material. This technique of foam layer formation is useful when it is desired to form the foam layer in place to avoid the necessity of handling a separate foam layer or avoid the need for a separate adhesive material to attach the foam to the adjacent layers (i.e., the polymer often has good adhesive properties on its own). It is also useful when it is desired to have a foam layer of non-uniform thickness. In some cases, the pressure from the volumetric expansion can be used to help form the final shape of the panel when confined in a mold with the decorative layer pressed against the mold surface by the expanding foam material.
Some decorative layers have perforations formed through their thickness as part of a decorative element for the interior panel. For instance, stitched threads may be sewn through the decorative layer, or the perforations themselves may be provided for aesthetic purposes. Introducing a liquid foam precursor between two layers of material is problematic when one of the layers includes perforations, as the liquid will sometimes flow into and/or through the perforations, making the foam layer undesirably visible from the decorative side of the panel when finished.
U.S. Pat. No. 7,851,039 to Boinais et al. discloses an interior trim piece that includes a seal element that is applied on the lower surface of a skin layer to help seal stitch holes when a foam layer is subsequently formed there. The seal is applied locally—i.e., only at the location of the stitching where needed to function as a seal—and is sometimes in the form of a tape layer that is applied along a stitched seam.